1. Field of the Invention
This invention pertains generally to continuously variable transmissions, and more particularly to a compact inline continuously variable transmission.
2. Description of Related Art
A Continuously Variable Transmission (CVT) is a type of transmission that can be traced to the 1800's. An early example can be found in U.S. Pat. No. 583,402 which is incorporated herein by reference in its entirety. Examples of more modern CVTs can be found in the following U.S. patents, which are also incorporated herein by reference in their entirety: U.S. Pat. No. 5,470,285; U.S. Pat. No. 6,293,888; U.S. Pat. No. 6,213,907; and U.S. Pat. No. 6,280,357.
Continuously variable transmissions generally utilize a pair of adjustable pulleys, including a primary pulley and a secondary pulley. The primary pulley is connected to the prime mover (e.g., an engine) and the secondary pulley is connected to the drive train of the vehicle, typically through a clutch. Generally, a drive belt interconnects the pulleys and transfers power from the primary pulley to the secondary pulley by means of frictional contact between the drive belt and the pulleys. Typically, each pulley is constructed from two flanges and each flange has a conical side surface to define a generally V-shaped gap between the flanges. At least one of the flanges is movable along the axis of the shaft to allow the gap between the flanges to be varied. The transmission ratio of the CVT can be varied by changing the effective gap width between the flanges of the two pulleys. Doing so varies the radial position of the drive belt in each pulley, thereby allowing for continuous adjustment of the drive ratio between the shafts and, therefore, between the engine and the drive train.
Movement of the flanges is achieved generally through a hydraulic servo, or other mechanical or electromechanical means, which controls the force on the belt or chain. Increasing fluid pressure causes more fluid to displace the flange to move axially and thus increases the effective diameter of the pulley. As fluid pressure is decreased, the flange moves along the shaft in the opposite direction due to the tension on the belt, thus decreasing the effective diameter of the pulley. Generally, the effective diameter of the primary pulley is moved in one direction as the effective diameter of the secondary pulley is moved in the opposite direction.
Most vehicles using CVTs employ a non-inline transaxle configuration similar to that schematically shown as 10 in FIG. 1. However, with the development of high torque chain elements for the CVT, placement in longitudinal vehicle powertrain orientations is unavoidable for the reason that most high torque vehicles are front engine and rear-wheel drive. However, typical CVTs with a ratio range of five or six have a pulley set with overall dimensions larger than the tunnel of the vehicle, and input and output shafts that are ten inches or more apart. These characteristics make implementation in rear-wheel drive vehicles difficult or impossible. In an automobile installation, space constraints limit the volume into which a transmission can be installed and thus limit the availability of using a belt or chain type CVT. Because a typical CVT utilizes a pulley assembly constructed from two pulleys positioned on parallel shafts and linked with a belt or chain, the minimum width required to install a CVT is determined by the size of the belt and pulley assembly. Rear wheel drive automobiles, however, offer only limited space in the transmission tunnel for the installation of a transmission, especially because the transmission tunnel in such automobiles is underneath the forward section of the passenger compartment. Typically, this space provides greater length than height or width.
Therefore, CVT configurations must be sufficiently compact and efficient to allow for practical use in rear-wheel drive vehicles. Such designs would necessarily have coaxial input and output shafts for placement in longitudinal configurations. However, conventional CVT designs using a combination of chains and gear sets to produce co-axial input and output shafts decrease efficiency and are still no smaller than the wide ratio range CVT pulley set. Toroidal CVT applications have good size properties, but are low in efficiency and much more complicated and are difficult to control and manufacture.
Another approach can be seen in U.S. Pat. No. 5,470,285, incorporated herein by reference in its entirety. In one disclosed arrangement, the power input shaft to the CVT system is coaxial with a power output shaft from the CVT system; that is, the axis of the power input shaft is in the same longitudinal direction as the axis of the power output shaft. Such a configuration allows the CVT to be installed into a rear-wheel drive automobile configured to use a conventional multi-gear transmission without requiring modification to the transmission tunnel or to the drive train. While the foregoing inline CVT configuration is compact, the configuration is complicated and decreases efficiency. U.S. Pat. No. 4,672,863 discloses a CVT connected to an auxiliary transmission, but configuration does not address the need for a compact assembly for rear-wheel drive vehicles.
Therefore, there is a need for a new CVT configuration that is sufficiently compact and efficient to allow for practical use in rear-wheel drive vehicles, including heavy duty vehicles. The present invention satisfies those needs, as well as others, and overcomes limitations in conventional longitudinal CVT configurations.